Field of Invention
The present invention relates to a capacitive power conversion circuit; particularly, it relates to a capacitive power conversion circuit capable of performing bi-directional current or voltage scaling conversion. The present invention also relates to a charging control method for use in the capacitive power conversion circuit.
Description of Related Art
FIG. 1 shows a prior art charger circuit (charger circuit 1) which comprises an adaptor 11 capable of directly charging a battery 50. The adaptor 11 can provide a charging current through a cable 20 (for example a USB cable) and a load switch 40 to the battery 50 to charge the battery 50 by a constant current, wherein the DC current IDC and the charging current ICHG are substantially the same. However, when using a USB standard cable, the maximum current is limited by the cable current rating, which is 5 A or lower, and therefore a longer charging time is required. If it is desired to raise the charging current, for example to 8 A or higher to expedite the charging time, a specially-designed fast charging cable with a larger diameter is required. However, it is inconvenient to use the fast charging cable, because first, it is a non-standard cable, and second, the fast charging cable is less flexible for accommodation due to its larger diameter.
FIGS. 2A and 2B show a prior art charger circuit (charger circuit 2) which includes a switching conversion circuit 60. In a charging mode, the switching conversion circuit 60 converts the power provided by the adaptor 11 (for example but not limited to 5V, 9V, or 12V VBUS compliant with USB PD specification) to a charging current ICHG to charge the battery 50 by a constant current. In this prior art, the charging current ICHG may be larger than the DC current IDC. And in a supply mode, the prior art shown in FIG. 2A can support the USB OTG (On-The-Go) specification. Referring to FIG. 2B, the switching conversion circuit 60 can reversely convert the battery voltage VBAT into an output power compliant with USB OTG specification (for example compliant with USB or USB PD specification) and supply the output power to a USB OTG load (not shown). A drawback of the prior art circuit in 2A and 2B is that it is very difficult to optimize the choices of the specifications of the inductor and switches (both not shown) of the switching conversion circuit 60 so that critical parameters such as the charging current, current ripple amplitude, conduction resistance of the switch, power conversion efficiency and etc. can be optimized.
Compared to the prior art in FIG. 1, the present invention is advantageous in providing a scale-up charging current for charging a battery to shorten the charging time, while a standard cable such as a USB compliant cable can be used, through which only a relatively lower current is allowed. Compared to the prior art in FIGS. 2A and 2B, the present invention is advantageous in not requiring an inductor, having a smaller size, lower cost, and easier optimization for component selections to maximize power conversion efficiency.